Thread cutting mechanism



'F. NELL THREAD CUTTING MECHANISM July 2, 194.

.Filed Feb. 23, 1944 4 Sheets-Sheet 1 3mm fredenzt fli,

July 2, l6. F. NELL 9 THREAD CUTTING MECHANISM Filed Feb. 23, 1944 4Sheets-Sheet 2 woe/whom July 2,1; F. NELL 2,403,015

THREAD CUTTING MECHANISM I Filed Feb. 2s,' 1944 4 Sheets-Sheet s @WVW July 2 1946. F. NELL a THREAD CUTTING MECHANISM 4 Sheets-Sheet 4 Filed-Feb. 23, 1944 fly WWI/r 71 eZZ,

v fr'denz'c Patented July 2, 1946 moans THREAD CUTTING MECHANISM Frederic Nell, Waynesboro, Pa., assignor to Landis Machine Company, Waynesboro, Pa., 7 a corporation of Pennsylvania Application February 23, 1944, Serial No. 523,599

26 Claims.

Thisinvention relates to thread cutting mechin prior art developments, including those disclosed in Patents 2,283,280, May 19, 1942, and 2,291,744, August 4. 1942, to Frederic Nell and Patent 1,811,802, June 23, 1931, to Samuel F. Newman, respectively, For the purposes of this explanation I have shown such improvements as applied to a collapsible tap of the receding type, for generating an internal thread on pipes or other tubular members commonly employed in the oil, and steam fittings equipment supply industries. However, as will become evident from the following detail description, the novel features of my invention are also applicable to die heads for cutting external threads, and, in said description, and in the claims the expressions thread cutting mechanism and collapsible tap are intended to generically include both of these well known types of thread cutting machines.

In thread cutting mechanisms of the prior art, such for instance as that shown in Patent 1,811,- 802, the means for producing the thread taper embodies a large number of contacting, relatively sliding parts between which it is difficult and expensive to maintain close fits during the life of the'machine. This was particularly true of the operation of the tripping cams'and gibs which control the accuracy of the taper being generated and, it was found that, over a period of time, the wear between these parts caused irregular tapers. The importance of a high degree of accuracy in the operation of such mechanisms becomes apparentin view of the fact that the present trend of industry in this respect has been accelerated by standards recently established for Army and Navy Aeronautical and Ordnance requirements, and the development of more eflicient gauges and thread checking means.

It is, therefore, one of the primary objects of my invention to provide a thread cutting mechanism, in which the number of relatively sliding elements comprised in the taper control means is reduced to a minimum, and in which such sliding movements are comparatively short, so that the final taper is not affected by such wear as l vides certain important practical improvements tages of the invention.

does occur, thus assuring a high degreeof accuracy and uniformity of thread taper in the operation of the mechanism.

Another-important object is to provide a taper control mechanism in which lost motion is eliminated to thereby insure a continuous and uniform taper of the thread being generated.- I

A further object of the invention is to provide a compact, rugged and rigid construction'which embodies a comparatively small number of elements of simple mechanical forms for the control of position, diameter, taper and length of the thread to be cut.

Anadditional object is to provide a novel multiple section plunger mechanism for receding and retracting the thread cutting elements, and novel means for functionally co-ordinating a thread taper controlling lever therewith.

It is also an important object of the invention to provide a collapsing or retracting spring which is not affected by the receding action of theplun er mechanism and remains under a single, uniform tension for all diameters to be threaded within a predetermined range. V r

'A very practical objective of my present improvements is to materially simplify and increase the serviceable life of the plunger latching means, in mechanisms of this kind, and to provide a latch keeper element in the form of an adjustable and readily replaceable, inexpensive repair part.

The invention has for another of its objects the provision of a sliding, adjustable, latch tripping key, whereby different thread lengths may be out without disturbing -the diametrical adjustment of the cutter actuating head.

As a further contribution to the art my invention provides a novel means for adjusting the fulcrum axis of the taper control lever so that the threadtaper may be readily varied, plus or minus, from apredetermined norm.

Preferably, I also propose to employ a cutter or tap carrying head which is removably secured to the end of the tool body, so that heads, with different forms and arrangements of the cutters, may be interchangeably used with a single body, thus materially increasing the utilitarian advan- 'In general, it is the aim and purpose of my present invention to provide a thread cutting mechanism as above characterized, which is distinguished by simplicity of design, low initial and upkeep cost, positive and efiicient functional operationfland the ability to out threads in an ex- ,'.tensive range of tapers with maximum accuracy ing elements retracted and the parts of the mechanism in collapsed position. v

Figure 3 is a fragmentary horizontal sectional view taken substantially on the line 33 of Figure 6, the parts being latched in the's'et position of Figure 1. g

Figure 4 is a similarsview, with parts in the collapsed position of Figure 2. v H

Figure 5 is a transversesectional-view taken substantially on the line E -5:01 Figure}.

28 and 29, respectively, of the multi-sectional plunger structure have unitary and relative reciprocating movement in the bore 21.

The intermediate plunger section 28 is connected with the front section 22 of the plunger by means of the adjusting rod 38, the forward end 3| of which has threaded engagement with a threaded'section of the bore 32 of the plunger section 22. Adjacent to its rear said screw is formed with spaced collars 33 and 34 between which the slotted wall of a socket formed on the forward end of plunger section 28 is received.

Figure 6 is a similar sectional-view taken substantially on the line B& of Figure 31 Figure 7 isan end elevationo'i the detachable bracket showing the fulcrum means for the taper control lever mounted therein; and

Figure'il is a detail view on an enlarged scale showing thefulcrum adjusting means for varying the thread taper.

a In these drawings, by way of example, I have fully disclosed one concrete embodiment 'of a preferred form of the several novel features of my presentinvention, as applied to a well known type b of receding collapsible tap. Thus, asain the above referred to Patent No. 1,811,802 the elongated, cylindrical body Iii is provided at its rear end with a reduced shank extension H 'for connection with the vertical or horizontal spindle of a drill, lathe or other suitable driving machine. This tap body is circumscribed by a longitudinally slidable sleeve 2 having a plurality of radially projecting apertured lugs [3 adjacent toits forward end. 7 A ring I4 is adjustably and rigidly supported in forwardlyspaced relation from the sleeve !2 by the rods 1-5 having studs 56 at their forward ends threaded into the ring l4. The threaded rear ends or these rods extend through the apert'ured lugs Idfandare adjustably locked in connection therewith by the nuts I! tightly engaged with opposite side faces of saidv lugs.

The sliding sleeve is the primary control means for the tap receding and retracting mechanism and, to the extent above des cribed, the present disclosure is characteristic of current practise in. the art. I

To the forward end of the body ill, and, in effect, constituting an integral extension thereof,

the tap carrying head l ft is, preferablydetachably secured by a plurality of belts, in the manner shown at [9 in Figures 1 and 21 This head carries the" radially adjustable taps, chasers, or cutting elements 20 having" obliquely inclined innenends provided with keyways 2! with which similarly inclined keys 24, formed on the tapering truncated head 23 of the forwardplunger section 22, are adapted to coact in the customary well known manner to radially expand, recede and re- .tractsaid cutting elements. The head la. base longitudinal bore 25 in the other end ofwhich a guide sIeeyeZB for theplunger section 22 is fixed. .Thebody Ill has an-v axial. bore. 21 extending substantially the, entire. length thereof and with the forwardend of which the bore 25 of thehead I I8 is in aligned connectiom The other sections center of bore 21.

disclosed in Patent No. 2,233.280 above identified.

Referring now to Figures 3 and 4 of the drawings, it will be noted that the plunger section 28 includes a short cylindrical forwardend portion 39 and a relatively long rearwardly extending semi-cylindrical part 45, the curved surface of which has the saline radius as the part 39 and describes an arc of less than to thereby provide a'flatinner surface 5! at one side of the axial Similarly the rear plunger section 29 includes a rear cylindrical portion 42 and a relatively long forwardly extending part 43, corresponding in cross-sectional shape and dimensions to the part 49 of plunger section 28,

and having an inner flat-face M at the opposite side of the axialcenter of bore 21 and in opposed,

plunger section 29 is also formed with a reduced cylindrical terminal extension 45 at its rear end 2 fora purpose which will be presently explained.

The face ll of plunger section provided,

intermediate of its ends; with a transverse slot 45 in which a block e'lis freely slidable. One end of the taper control lever 43 is positioned between the parts 42 and 43 on the axialeenter line of the plunger mechanism and is provided on its opposite side faces with pivot studs 45 and 5!}, respectively, having their axes spaced apart longitudinally of said lever. The stud 65 is pivotally engaged in a recess or opening 5! in the sliding block 41 while the other stud 50 is similarly engaged in the recess or opening 53 of a bar 52. perpendicularly disposed relative to the plunger axis andwithin recess 44' formed in the inner face M'of the part 43 of rear plunger section 29. One end of this bar 52 extends transversely through a short longitudinal slot 5!; in one side ofthebody It! while the other end portion of said bar extends through a relatively long slot 55 in the opposite side of said body. This slot is also comparatively wide, as seen in Figure 5, to accom modatethe lever 48 for movement relative to the bar 52. The opposite ends of the bar 52, have sliding contact with the base walls of diametrically opposed internal grooves 56 in the wall of the sleeve 62 and in the set condition of the plunger mechanism have abutting contact with fiat "shoulders 58 formed on the inner ends of cylindrical studs or pins. 51 fixed in. the wall of said sleeve. Bar 52 thus acts to limit forward moveing 59 through which the other or outer end of the lever 48 projects and centrally thereof this opening is cylindrically enlarged, as at 6!), to receive a cylindrical boss 62 formed on one end of a bracket member 6|. This bracket member is of general rectangular form, as seen in Figure '7, and is centrally provided with a cylindrical bore 63 extending therethrough in concentric relation to the boss 62. This bore and the boss are axially bisected by a slot 64 in which the end of lever dais received. The other end of the bracket is,

preferably, provided with a separable cover plate 65 for the bore 63 and slot 64 and said plate is retained in assembled relation with the bracket body and said assembly detachably secured in rigidly fixed relation to the sleeve I2 by means of a plurality of screws 65.

With particular reference to Figures 1, 2 and 5, it will be noted that the outer end of the taper control bar 48 is provided with a longitudinally elongated, rectangular slot 61. This slot receives an adjustable fulcrum block 68 for said end of the lever, said block being provided with axially aligned, oppositely projecting trunnions 69 pivotally engaged, respectively, in the recess or opening i! of one of a pair of like semi-cylindrical members l9, slidably engaged with the walls of the bore 63 in bracket 6 I.

For the purpose of regulating the operation of the plunger mechanism in order to vary the thread taper in small increments, as may be required, there isstamped in oneface of the lever 48, at one side edge of the slot 67, a graduated scale 12 (see Figure 8). Adjacent to the scale 12 a key lug 13 projects into the slot 51 and is adapted for engagement in anyone of the notches or recesses 14 formed in the edges of the rectangular block E8. 'It will be noted that a single recess is provided in each edge of the rectangular block and these recesses are located at relatively different distances from the edges of the block which extend at right angles to the edge in which the recess is formed, In the drawings the block 68 is shown with one of its edges in register with zero on the scale F2 for a basic taper, say inch to the foot. By adjusting the position of block 68 in the slot 6'! and engaging the key lug l3 in another selected recess 14, another edge of the block is positioned relative to the scale to vary the taper plus or minus. Of course, for the pur-' pose of making more minute adjustments, additional recesses may be provided in the edges of the block. Such taper variation is caused by the fact that adjustment of block 68 variably positions the fulcrum trunnions 69 and members I0 lengthwise of lever 48 with respect to the pivotal connection 49 between said lever and plunger section 28, which in turn variably controls the extent of receding movement of plunger sections 28 and 22 relative to plunger section 29,

as will presently be more fully explained.

A strong coil spring 15 in the bore 15 of the shank extension ll of the body has its closely engaged forward end convolutions l1 threaded on a screw stud projecting from the rear end portion of the plunger section 29. The closely engaged rear end convolutions 18 of said spring are engaged with the external threads of a tubular nut I9 which is also internally threaded to receive the screw 89 whereby said nut is tightly held in engagement with the seat 8| at the rear end of bore '16. The sole purpose of the spring 15 is to rapidly retract the composite plunger mechanism as a unit after the receding function thereof and the threading operation has been completed.

In order to retain the several parts of the plunger mechanism in the set condition of Figure l, at the start of the threading operation, I provide a novel latching means therefor, and an improved latch tripping device, which will now be described, with particular reference to Figures 3, 4 and 6 of the drawings.

The reduced rear end 45 of the plunger section 29 is provided at opposite sides thereof with the transverse grooves 82 connected at one of their ends by a circumferential groove 93 (see Figure 6). In these grooves a substantially U-shaped latching member 84 is engaged and yieldingly urged outwardly, to a normal postion, in which its intermediate portion projects beyond the periphery of the plunger end 45, by a spring 85 seated in a recess 86 in the plunger. 1 r

The latching member 84 is adapted to coact with a relatively fixed keeper. In the present instance this keeper is in the form of a metal ring or annulus 81 which, I have found, has certain desirable practical advantages in the operation of the mechanism. This keeper ring is of appreciable width and is fitted into the rear end ofthe bore 21 in the body in. The external di- "ameter of the ring is such as to permit of its rotative adjustment relative to the bore and it i provided, substantially mid-way between its end edges, with a plurality of circumferentially spaced openings 83 having inwardly beveled edges 69. With the edge of one of these openings the "inner tapered end 9| of a screw 99 threaded in an opening 92 in one side of the body I0 is tightly engaged to securely retain said ring in adjusted position, and with one end thereof in abutting contact with the rear end Wall of the bore 21. In this manner the other end edge of the keeper ring is definitely positioned for cooperation with the latch member 84 and in relation to a flattened face 95 on the enlarged inner end 94 of a latch actuating pin 93. This pin is transversely movable in the opening 96 in body I0, the inner end thereof being counterbored, as at 91, to receive the'enlarged end 94 of said pin. This end of the pin is received in a recess 94' in the end of the part 42 of piston section 29 in the retracting movement thereof (see Figure 4). The outer end of the pin 93 has a-beveled or inclined face 98 for coaction with a latch tripping key carried by the sleeve l2.

In alignment with the latch actuating pin 93 the wall of the sleeve I2 is provided with an internal longitudinally extending slot 99 to receive an elongated tripping key I09 of T-shaped form in cross section (see Figure 5). At its inner side this key has longitudinally spaced surfaces It! and [02, respectively, reversely inclined longitudinally of the key. The key includes an end section 593 of reduced thickness extending beyond the surface NH and so positioned relative to the outer end of pin 93 that it will not actuate the latter. The surface I92 is located at the other end of the key. Thus, by reversing the key, end for end, in the slot 99 said key will coact at the proper time with latch actuating pin 93 :7 in :cutting ieither long or short thread lengths. The extension I 9-3 also assures the necessary bearing surface for thespaced locking screws I 04 to securely fix the key in either of such'positions in the groove 99.

The sleeve I2 is held'against rotative movement relative to the body I9-to prevent frictional binding pressure against the ends of bar 52 and to retain thetripping key ID!) in accurate alignment with latch actuating pin 93, by a sleeve guiding :key I 05 which is securely fixed in the longitudinal groove I03 in theperiphery of the body I9. This key projects outwardly from the body andis engagedin theaccurately milled internal key-way I01 of the sleeve I2 (see Figure 6). r

The key IE5 is providedat-its forward end with a series of rack teeth I98 with which the teeth of a segmental pinion IIII formed on "one :end of a ,re-setting'lever 4-09 .are adapted to soact. ,This lever :-is pivotally mounted, in an opening HI in the sleeve, I2, upon the pin I I2 which is suitably fixed at its opposite ends in said :sleeve.

Having describedthe-eoeoperative relationship -of the several elements of my new thread cutting wrnechanism, the operation thereof may be readily understood. Referring first to Figures 1 and 3 oil-the drawings where the'several parts are shown in relative =p-osit-ion after the multi-sectioned plunger has been set 'to-expand the cutters or ohasers toposition for engagement with the work, assaid cuttersenter the end-of the pipe or tube, the ring M-engagesthe-pipe end or other stationary .part. Therefore, as the thread cutting operationprogresses, the connecting rods I5 move the sleeve 42 rearwardly on thebody III. The upper end" of taper control 1ever-48 being pivoted to the relatively fixed -bar 52, the outer end of said lever also moves rearwardly :and outwardly, the fulcrum members lfl'forsaidend of the lever sliding .freely inthe bore "63. It will also be obviousthat the-pivot connection between said leverand plunger section 28 is angularly moved in-a :rearward direction relative tothe pivot connection 59 between said lever and the fixed bar 52 the block 4''! slidingtransversely in the groove 45. As the plunger section .28 is connected by adjusting rod39 with the plunger section 22, in this relative 'angular movement "between the pivots 4:9 and 50, said plunger sections will move rearwardly-ass,1unitrelative to the rearplunger section 29. The plunger 'head 23 is thus drawn rearwardly to recede the cutting elements 20 or more the same inwardlywtowards the plunger axis synchronously with the generationof the thread.

--I-'he threadcutting operation and rearward movement of the sleeve I'2 continues, until, in accordance with the setting of the -key I for a ,pre-determined thread length, one of the -inclined surfaces IOI or I02 on the key contacts the inclined face 98 on the'outer end of pin 93 and presses said pin inwardly. As seen in Figure 3 this inward. movement .of pin 93 will force the latch member inwardly on the plunger end 45 against the resistance of spring 85, thus disengagingsaid latchmember from contact with the forward end edge of the keeper ring 81. Substantially simultaneously with the tripping of -:latch member -84 the spring I contracts and moves the three plunger sections 22, 28 and 29 rearwardly as a unit, thus retracting the cutting elements from the work to the position shown in Figure 2. This movement is limited by contact of .theend 45 of plunger section 29 with the rear end'wa-ll-of bore 21 inthe-body l0.

"8 From comparisonaof Figures .1 -andr2 it 'will be noted that'in therecedingactionof the; plunger mechanism, as the sleeve I2 moves rearwardly,

the outeiaend of lever 48 turns or pivots relative to the fulcrum members 70 as saidmembers-slide ment of the fulcrum-block for said lever for-a desired taper and the adj ustmentof tripping key "I60 fora desiredthread length.

In the final cutter retracting or collapsing action of the plunger mechanism the end '45 of plunger section .29, oarryingthe latching member 84, is positioned within the tubular keeper member or ring 81, as seen inF'igures 2 and 4,-said plunger end having a length 'slightly exceeding the width of the ring to avoid possible mutilation of the forward-end edge :of the ring by violent impact of the end shoulder of plunger part-42 therewith.

In the retracting action the ends of bar 52 are moved rearwardly relative to sleeve I2 in the grooves 55 thereof one end of said bar beingpositioned relative to the rear-end :ofslot 54 in the body II), substantially'asseen in Figure 2. It will also be noted'that, by the sliding movement of sleeve I2 which controls the'receding action-the pins 51 carried by said sleeve iare now positioned in rearwardly spaced relation from the ends-of bar-52,

To re-set the mechanism with the parts thereof relatively positioned as seen-inFigure "l, the sleeve I2 is moved forwardly on the tool .body III, from the position of Figure 2,either by means of --a yoke'operating mechanism, (not shown), exerting pressure against the rear end of the sleeve, or by gravity movement of the yoke if the tool is operated in a vertical position. This movement of the sleeve is, of course, accompanied by a corresponding movement of ring I4 and bracket/6|, which returns or restores lever I8 to the position of Figure 1. Such forward movement of the sleeve I2 is finally arrested by the engagement of pins 51 with the rear edge of bar 52 and at this time the teeth Ilfl of the re-setting lever I09 are in position to engage rack teeth I08 on 'key'IU5.

The rearward movement of sleeve -,I2 which caused the receding actionof the plunger mechanism has now all been removed and the parts are in position for the final re-setting step. This 7 may be accomplished in either one of two ways, viZ., by applying further pressure-against the rear end of, sleeve I2 or by moving lever I09 from the position of Figure 4 to the positionof Figure-3, relative to said sleeve. In'either case, a further forward movement of the sleeve causes the pins 51 to exert pressure against the rear edge "of bar 52, said bar and sleeve now moving as a unit with respect to the body I9. Since bar 52 .is'keyed to the rear plunger section 29 and connected with plunger section 28 through lever 48, moving with said sleeve, the three plunger sections .29, 28 and 22 are now moved forwardly as a unit. This unitary plunger movement occurs in opposition to the resistance of spring 15, whichis expanded and placed under tension, simultaneously with the radial expansion ,of cutter elements :22 to op erative'position by the plunger ahead 23.

This forward expanding action of the plunger mechanism continues until the rear edge of latch member 84 coincides with the forward edge of the relatively fixed keeper ring 81. Spring 85 then acts to force the latch member 84 outwardly and .mechanism are now fullyrestored to the relative positions illustrated in Figures 1 and 3, in condition for another threading operation.

From the above description, the several novel features of my improved thread cutting mechanism, as well as the manner in which the mechanical parts thereof are functionally co-related or co-ordinated to accomplish the intended practical results of the invention, will be clearly and fully understood. Of primary importance to the realization of a high degree of accuracy in the cutting of taper threads is the material simplification which I have devised in the taper control train of mechanism in contrast with prior tools of this kind. Thus, I employ a comparatively small number of simply constructed parts which are incorporated in a compact organization, in which lost motion between relatively moving parts has been completely eliminated. Also, sliding motion between relatively movable and stationary parts has been reduced to a minimum, whereby taper accuracy will not be seriously affected by frictional wear, and the receding action of said mechanism takes place entirely independently of the retracting or collapsing spring or other means yieldingly resisting such action, which assures uniformity. of thread taper. Since the plunger section 29 has but one latched position, the spring will have the same tension for all thread tapers and diameters within the range of the tool. These desirable functional attributes of my invention are, in large degree, due to my novel multi-sectional expanding, receding and retracting'plunger mechanism and the means which I employ for co-operatively connecting the taper control lever therewith.

'It will further be noted that in the present construction I avoid the use of wedges, eccentrics, cams, or the like having extensive wearing surfaces, as in the patents above referred to, and which, after a short period of use, produce an inaccurate taper or require the addition of complicatlng adjusting devices.

latch member iifl. Therefore,in all probability, this keeper ring will out-last the serviceable life of the tool. However, should it become unduly worn, it may be readily replaced at very nominal expense. r

This adjustable latch keeper insures unfailing outward expansion of the cutting elements 20 in each re-setting operation of the plunger mechanism to precisely the same cutting position at the start of each threading operation, with positive coaction between latch member 86 and the keeper ring to lock said mechanism against collapse. Therefore, after tripping key I08 has been properly adjusted on the sleeve l2, as above explained, in accordance with the predetermined thread length to be cut, each operation'of the tool will produce accurately tapered threads of exactly the same length on the work.

Further, it will be seen that, as in the-patent last referred to, I provide a simple and easily adjustable means to vary the taper in; small increments, plus or minus from a basic value, but,-unlike said patent, this adjusting means is normally inaccessible and is of such construction that accidental or unintentianal disturbance of the adjusted setting is impossible.

Finally, it may be said that my present improvements provide a greatly simplified, compactly and ruggedly constructed thread cutting mechanism of this type, embodying new principles of construction and operation, whereby, as distinguished from prior efforts in this art, I am able to acceptably meet the exacting demands of modern industry for extreme accuracy and consistently uniform results.

' The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. The present embodiment is'the'refore to be considered in all respectsfa's illustrative and not restrictive, the scope of the invention being indicated by the appendedjclaims rather than by the foregoing description, and all-changes which come within the meaningand'range of equivalency of the claims are therefore intended to be embraced therein;

7 What is claimed and desired to be secured by United States Letters Patent is:

' 1'. In a thread cuttingmachine, a body provided witha plurality of thread cutting elements radially movable towards and from a common The accurate control of thread length provided by ,my'invention, in the plunger latching means and the adjustable and reversible tripping key therefor, is also an important contribution to the practical utility of such tools. In this connection, and as 2,291,744, the simple and inexpensive type of adjustable latch keeper ring 8'1 is to be particularly noted. Thus, when one point on the end edge face of'the ring shows signs of wear, said ring distinguished from Patent may-be rotatively. adjusted and the end of screw engaged in another of the openings 88 to present another edge surface portion of the ring for engagement by the latch member 84. After this adjusting operation has been repeated for as many times as there are openings 88 in the keeper ring, the position of said ring in the bore 21 of tool body [0 may then be reversed to locate the other end edge face of said ring for adjustment in a similar manner with respectjto the center, plunger mechanisn'i comprising relatively movable parts, mounted in said body and one of said parts having an axially movable plunger head cooperatively connected with said cutting elements to recede the same from the'work during the threading operation, means for releasably latching the plunger mechanism against movement relative to the body to retain the cut ting elements in expanded operative positions, and means interposed between and connected with the relatively movable parts of the plunger mechanism to independently actuate the plunger head and recede the cutting elements from the work in predetermined ratio to the progressive thread cutting action of said'elements to form a tapered thread. 1

2. The thread cutting machine defined in claim 1 in which saidrelatively movable parts of the plunger mechanism are operatively mounted in sliding contact with the wall of a uniform diameter bore in said body; 1

.3. The thread cutting machine defined in claim 1,,and an operating member for said last named {means longitudinally slidable on said body.

'4; The thread cutting machine defined in claim 1, together with a collapsing spring connectedto one of said plunger parts, and means for releasingsaid latching means at the end of the receding movement of the cutting elements, whereby the plunger mechanism is moved as a unit in one direction to collapse said elements to inoperative position.

5. In athread cutting machine, a body-provided with a plurality of thread cutting elements radially movable towards and from a common center, plunger mechanism including complementary parts of equal diameters axially movable in said body relatively to each other and a plunger head rigidly connected to one of said parts and operatively connected to the inner ends of said cutting elements to expand, recede andcollapse the same, a, taper control lever operatively connected at one of its ends with each of said plunger parts, and means mounted on said body and'operatively connected with the other end of said lever to synchronously actuate said lever'in the progressive thread cutting action of said elements to impart an independent axial movement to the connected plunger part and head and recede the cutting elements from the work to form a tapered thread.

6. The thread cutting machine defined in claim 5 inwhich saidrelatively movable plunger parts have transversely spaced apart opposed end portions and said taper control lever is positioned therebetween.

7. The thread cutting machine defined in claim 5 in which said taper control lever has a fixed pivotal connection with one of said plunger parts and a pivotal connection with the other of said plunger parts which is angularly movable in relation to said fixed pivot and with respect to the plunger axis, in the actuation of said lever.

8. In a collapsible'tap of the receiving type, a body having a, cutter head provided with radially expansible and retractible cutting elements, plunger mechanism mounted in said bodyincluding complementary parts of equal diameters axially movable relative to each other, means forlexpanding and retracting the cutting elements, o'peratively connected mom of saidplungerparts, a thread taper control lever having a fixed pivotal connection to the other of said plunger parts,a transversely shiftable pivotal connection between said lever and the first named plunger part, spaced from said fixed pivot longitudinally of the lever, and means operatively connected with said lever to synchronously actuate the same in the "progressive thread cutting action of said elements and impart an independent axial movement to thefirst named plunger part and said expanding and -retracting means in retracting direction to recede the cutting elements from the work and form a tapered thread.

9. The collapsible tap defined in claim 8, together with a collapsing spring urging the plunger mechanism to normal position to collapse the cutting elements, and latch'means releasably retaining the plunger mechanism in expanding position including a latch'keeper membermounted in the plunger bore of said body. v

' 10. The collapsible tap defined in claim 8 in which said last named meansincludes a member movably mounted on said body, togetherwith a collapsing spring urging the plunger mechanism to normal position to collapse the cutting elements, an element rigidly connected with the plunger-part having fixed pivotal connection with said lever and adapted to coactwith 'sa'id'rii'e'm- "her, toaxially movethe plunger parts asaunit in opposition tosaid spring and expand the cuttingelements tooperative position and latch means for releasably'locking theplunger mechanism in the latter position" during the receding action thereof, 7 V V 11-. In a'collapsible-tap of the receding type, a body having a'cutter head provided with-radially expansibl and retractible thread cutting elements, plunger mechanism mounted in said body co acting with said'eleme nts to-expand, recede/and retract the same to collapsed position,--a-spring urging-said plunger mechanism to a normal cutter collapsing position, means for latching said mechanism against movement to said normal position to'retain'the cutting elements in expanded position, and means synchronously-operable with the progressive thread cutting-operation of said elements in the latter position of the plunger mechanism to recede said-elements from'the work, said means including a taper control lever operatively connected to relativelymovabieparts of the plunger mechanism, a sleeve slida-ble on said body, and fulcrum means for "one end. of said lever carried by said sleeve andjbodi'ly movable in the operation of said sleeve radially of'the plunger axis.

12. The collapsible tap defined in claim 11 together-with' a'xguide bracket enclosing said end of the lever audits fulcrum means and detachably secured to said sleeve. 7

13. The collapsible tap defined 'in claim 11 in whichsaid fulcrum means comprises a fulcrum locating "member adjustable lengthwise of the lever towardsand from the plunger axis to vary th thread taper. V

14. "Ihe'collapsible tap defined 'inclaim 11 togetherwith'a guide bracket secured to said sleeve, said fulcrum means including a fulcrum support mounted'on said bracket for movementradially of the plunger axis, a member havin a fulcrum stud engaged with said support, and means for afliustably connecting said member with said l'eyerto position the fulcrum stud lengthwise of the lever andvary the threadtaper;

'15. i'lhe'collapsible tap defined in claim 11 togetherwith means for tripping said latch mechanism at the end of the receding movement of thejcuttin elements, comprising an elongated kewhaving longitudinally spaced latch tripping portions .and means for reversibly and adjustably securing said key .to the sleeve'inparallel relation to the axis thereof.

"16. In a'c'o'llapsible tap., aibodyhaving a cutter head provided with radially expansibleand'ra tra'ctible thread cutting elements, a plunger mounted in said'body and operatively connected with said elements to expand and retract'the same, a spring urging said plunger in o'nadirection to retract the cutting elements to collapsed position, means for moving the plunger in the opposite direction to expand said elements to cutting position, and latch means to retain the plunger in the latter position against the action of said spring, comprisin a spring pressed latching element mounted on the plunger, and a relatively 'fixed keeper member adjustably mounted on said body and having a plurality of surface portions adapted to be selectively positioned for latching engagement with said latching element.

'l'IQThe collapsible tap defined in claim 16 in which said latch keeper member comprises a rotatively adjustable ring contacting the end-wall of the plunger b'ore'in said'b'ody and means is 'pro- 13 vided to retain said member in its adjusted position.

18. The collapsible tap defined in claim 16 in which said latch keeper member comprises a flat metal ring adapted for reversible positioning in the plunger bore in said body, in rotative contact with the circumferential wall thereof, and with one of its end edges in contact with an end wall of said bore, and means for securing said ring in any one of a plurality of rotatively adjusted positions to present a selected portion of the other end edge of the ring for latching engagement with said latching member.

19. In a collapsible tap, a body having a cutter head provided with radially expansible and contractible thread cutting elements, a plunger mounted in said body and operatively connected with said elements to expand and retract the same, a spring urging said plunger in one direct-ion to retract the cutting elements to collapsed position, means for moving the plunger in the opposite direction to expand said elements to cutting position, said latter means including a longitudinally slidable sleeve on said body, means to prevent rotative movement of the sleeve on the body, manually operable means carried by the sleeve and co-acting with a part of said last named means to slide said sleeve in one direction and move the plunger to expand said cutting elements and means for latching the plunger in the latter position.

20. The collapsible tap defined in claim 19 in which the means for preventing rotative movement of the sleeve includes a sleeve guiding key fixed to said body and having rack teeth at one end, and said manually operable means comprises a lever pivotally mounted on the sleeve and having a segmental pinion co-acting with said rack teeth.

21. In a thread cutting mechanism, a body provided with a plurality of thread cutting elements radially rmovable toward and from a common center, plunger mechanism including complemen taryparts axially movable in said body relative to each other, means operatively connecting one of said parts to the cutting elements to expand and recede the same with respect to the work, a taper control lever operatively connected at one of its ends to the said plunger parts, and means operatively connected with said lever to actuate the same and impart a synchronous axial movement to the latter plunger part in the progressive thread cutting action of said elements, to recede said elements from the work and form a tapered thread.

22. In a thread cutting machine, a bodyprovided with a plurality of thread cutting elements radially movable toward and frdm a common center, plunger mechanism mounted in said body including parts having independent coaxial movement relative to the body, means operatively connecting one of said parts to the cutting elements to expand and recede the same with respect to the work, means for releasably latching the plunger mechanism against movement relative to the body to retain the cutting elements in expanded operative position, and means operatively connected to the plunger mechanism to impart an independent axial movement to the last named plunger part in synchronism with the progressive thread cutting action of said elements and recede the cutting elements from the work to form a tapered thread.

23. The thread cutting mechanism defined in claim 22, in which said last named means comprises a lever pivotally and slidably supported at one of its ends on the body and operatively connected at its other end with each of said plunger parts.

24. For use in a collapsible tap having a body and a reciprocal tap expanding and collapsing plunger therein provided with a yieldable latching element; a keeper member adapted to be fitted in the plunger bore and having a plurality of surface areas for selective engagement with said latching element to retain the plunger in tap expanding position.

25. The invention defined in claim 24, wherein said keeper member is of cylindrical form and provided with an arcuate surface substantially concentric with its axis embodying a plurality of surface areas for selective engagement with said latching element.

26. For use in a collapsible tap having a body and a reciprocal tap expanding and collapsing plunger therein provided with a yieldable latching element; a tubular keeper member adapted to be fittted in the plunger bore to receive an end of the plunger when in collapsed position and having an end surface to coact with said latching element and retain the plunger in tap expanding position.

FREDERIC NELL. 

